The present invention relates to an electrodepositable coating composition based preferably on basic, thermally crosslinkable epoxy or polyurethane resins.
It is known to coat metallic articles by means of electrodeposition coating, use being made thereof both in the automotive industry and otherwise in the metal processing industry. The electrodeposition coating systems used for this purpose generally consist of an aqueous binder dispersion and a pigment paste.
Resins which are electrodepositable at the cathode are described, for example, in U.S. Pat. No. 3,617,458. These are crosslinkable coating materials which are deposited on the cathode. These coating materials are derived from an unsaturated polymer which comprises amine groups and carboxyl groups and from an epoxidized material.
U.S. Pat. No. 3,663,389 describes cationically electrodepositable compositions which are mixtures of certain amine-aldehyde condensates and a large number of cationic resinous materials, one of which materials can be prepared by reacting an organic polyepoxide with a secondary amine and solubilizing the product with acid.
U.S. Pat. No. 3,640,926 discloses aqueous dispersions which can be electrodeposited at the cathode and which consist of an epoxy resin ester, water and tertiary amino salts. The epoxy ester is the reaction product of glycidyl polyether and an unsaturated oleic acid. The amine salt is the reaction product of an aliphatic carboxylic acid and a tertiary amine.
Binders based on epoxy and polyurethane for use in binder dispersions and pigment pastes, moreover, are known in numerous embodiments. Reference may be made, for example, to DE-2701002, EP-A-261385, EP-A-004090 and DE-C 3630667.
For certain applications, the throwing power is inadequate with all of the systems known to date. In other words, the distribution of paint between readily accessible exterior surfaces and difficult-to-reach interior areas is inadequate. Hence, for example, economic coating of flat radiators requires complete coating of the cavities formed by convectors with, at the same time, thin coats on the exterior surfaces.